diff --git a/ttd.c b/ttd.c
--- a/ttd.c
+++ b/ttd.c
@@ -421,8 +421,8 @@ static void ParseResolution(int res[2], 
 		return;
 	}
 
-	res[0] = strtoul(s, NULL, 0);
-	res[1] = strtoul(t + 1, NULL, 0);
+	res[0] = clamp(strtoul(s, NULL, 0), 64, MAX_SCREEN_WIDTH);
+	res[1] = clamp(strtoul(t + 1, NULL, 0), 64, MAX_SCREEN_HEIGHT);
 }
 
 static void InitializeDynamicVariables(void)